1. Field of the Invention
The present invention relates to a belt for a continuously variable transmission, including a plurality of metal elements supported on a metal ring assembly having a plurality of metal rings laminated on one another and which transmit a driving force between a driving pulley and a driven pulley.
2. Description of the Related Art
A conventional belt for a continuously variable transmission is disclosed in Japanese Patent Publication No. 5-56415 and Japanese Patent Publication No. 2-22254. In the belt described in Japanese Patent Publication No. 5-56415, a plurality of mountain-range-shaped protrusions are arranged in a mesh shape on each metal ring. As a result, an appropriate friction coefficient that centers the metal rings and appropriate lubrication between the adjacent metal rings are ensured. In the belt described in Japanese Patent Publication No. 2-22254, a plurality of mesh-shaped grooves are formed on a surface of each metal ring. The friction coefficient between adjacent metal rings is reduced, which enhances the transmitting efficiency of the metal belt.
An inner peripheral surface of the innermost metal ring of the metal ring assembly is exposed to severe conditions relative to the other metal rings as it is brought into direct contact with saddle faces of the metal elements. Therefore, the durability of the innermost metal ring understandably plays a large role in influencing the durability of the entire metal belt. If mountain-range-shaped protrusions are formed on the inner peripheral surface of the innermost metal ring to enhance the oil-retaining property, the saddle faces of the metal elements are disadvantageously brought into contact with the protrusions and generate pitching (i.e., very small cracks), which, over time, grow larger and ultimately decrease durability.